UPDATE 1-Banamex uncovers new $15 mln fraud in Mexican bank unit

MEXICO CITY, Oct 14 (Reuters) - Citigroup Inc said on Tuesday it uncovered a $15 million fraud at Banamex, its troubled Mexican bank, related to a private security services company the bank operated.

The company, originally set up only to protect Banamex's board members and their families, was found to have been offering its services to third parties, a person familiar with the investigation said. The fraud related to expense claims submitted by the company, the person added.

The loss is the latest of a string of problems at Banamex. Citigroup said in February it uncovered at least $400 million in fraudulent loans that Banamex made to Mexican oil services company Oceanografia. That figure has since increased to more than $500 million.

The Mexican unit fired two bond traders after uncovering rogue trading last year and taken writedowns related to bad loans to Mexican homebuilders extended in the last few years.

Banamex USA is facing a U.S. criminal investigation involving possible violations of money-laundering laws, a source has told Reuters.

The responsibilities of Banamex's security unit widened over time to include providing services to Banamex senior executives, the source said. The unit also began providing services to outside parties, who may have been Banamex clients, the source added.

The security company is being wound down and its services will be provided by an outside contractor, Citigroup said in a statement.

Violence in Mexico has increased in recent years as the government has fought with drug gangs.

Many international companies provide top executives in Mexico with kidnap insurance and some security services, usually from outside contractors.

Mexico's President Enrique Pena Nieto took office two years ago, pledging to end the violence that has killed about 100,000 people since the start of 2007. Although homicides have fallen during his presidency, other crimes have increased, including extortion and kidnapping. (Reporting by Elinor Comlay, Editing by Dan Wilchins, W Simon and Jeffrey Benkoe)